In the manufacture of Large Scale Integrated (LSI) semiconductor chips on wafers, the ever-increasing miniaturization of the structures on the semiconductor chip are responsible in particular for imposing ever greater requirements on the production installations and manufacturing processes used for the manufacture of the semiconductor chips. The stability and reproducibility both of the production installations and of the manufacturing processes decisively influence the yield and productivity during semiconductor chip production. Even small deviations from a set-behavior of a wafer production installation during production can lead to considerable worsening of the yield, that is to say to a considerable increase in the defect rate of the semiconductor chips manufactured.
Consequently, a major aspect in the manufacture of semiconductor chips is to detect possible deviations from a set-behavior in a chip production installation or during a manufacturing process at a very early time and to take corresponding countermeasures. Consequently, the analysis and monitoring of machines, in particular of the chip production installations, and of the manufacturing processes takes on very great commercial significance. Furthermore, the analysis and monitoring of many process steps of the manufacturing process is of considerable significance, since it is usually only rarely possible to repair an intermediate product after a process step has been carried out. A functional test of a manufactured semiconductor chip is generally not scheduled until right at the end of the manufacturing process, which leads to very late feedback into the manufacturing process of the results obtained.
It is further known to provide in-line measurements of interim process results, for example of the layer thicknesses, the layer resistance or of line widths, etc., by means of Statistical Process Control (SPC). However, this leads to additional measuring steps in the overall manufacturing process and is consequently time-consuming and costly.
In Advanced Process Control (APC), data from internal and external sensors of the production installations are analysed in combination with measuring techniques used, including in-line measured data on intermediate products, as well as results of measurements on test structures, once the wafer has been completely processed, results of functional tests on the semiconductor chips, the yield of defect-free semiconductor chips, etc. In this way, both the stability of the production installations and the process stability can be increased significantly, and in this way so the production productivity and the product quality of the semiconductor chips manufactured can be increased.
In general, the semiconductor chips are manufactured several at a time on so-called wafers. These wafers are in turn grouped into so-called lots, in which a multiplicity of individual wafers are logistically combined for further treatment of the wafers and subjected together to semiconductor process steps.
For in-line measurements of intermediate process results as part of SPC, selections of random samples of wafers of a lot are performed. Test measurements, which relate either to the quality of the manufacturing steps of a manufacturing process or to the quality of the products manufactured, are then carried out on the selected samples of wafers.
According to the prior art, the sample selection generally takes place by means of so-called hands-on rules, i.e. an explicit, precise individual rule is prescribed and used as a basis for carrying out the sample selection. This may take place either by means of handling instructions, i.e. instructions as to how for example entire product groups are to be handled, or by means of explicit stop instructions in the process schedule, which concern selected lots of wafers. The sample selection is carried out separately after individual process steps.
U.S. Pat. No. 6,477,432 discloses a system for administering the quality control in a production installation for processing lots of products in processing for at least one product, which system has a manufacturing process and a Statistical Process Control (SPC) analyser.
U.S. Pat. No. 6,148,239 discloses a process control system which uses feedforward control threads which are based on material groups and which uses material tracking to take into account the variability of the processing in a process sequence.